This invention generally relates to toner compositions and their utility in electrophotography. More specifically this invention relates to toner compositions having a polymeric polyester dye component for development of latent electrostatic charge patterns.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic electrophotographic imaging process (U.S. Pat. No. 2,297,691) involves placing a uniform electrostatic charge on a photoconductive insulating layer known as a photoconductor or photoreceptor, exposing the photoreceptor to a light and shadow image to dissipate the charge on the areas of the photoreceptor exposed to the light, and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic toner material. The toner will normally be attracted to those areas of the photoreceptor which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This developed image may then be transferred to a substrate such as paper. The transferred image subsequently may be permanently affixed to the substrate by heat, pressure, a combination of heat and pressure, or other suitable fixing means such as solvent or overcoating treatment.
Toner and developer compositions including colored developer compositions are in wide use. These compositions normally contain toner particles consisting of resin and colorants, and carrier particles. The colorants usually are selected from cyan dyes or pigments, magenta dyes or pigments, yellow dyes or pigments, and mixtures thereof.
One of the main advantages of selecting organic dyes instead of pigments for color toner compositions resides in the provisions of increased color fidelity as the dyes can be molecularly dispersed in the toner resins. To obtain a homogeneous dispersion, it is generally necessary to build into these molecules certain substituents for enhancing their compatibility with the toner resin. Unless the dye molecules are substantially fully compatible with the toner resins, they have a tendency to aggregate with time, especially when subjected to heat, pressure and humidity thereby resulting in a loss of color fidelity. Additionally, the low molecular weight of the dye molecules causes a high lability or mobility of the dye molecules in the toner resin resulting in undesirable bleeding of the dyes.
Of particular interest with respect to the present invention are toner compositions which include a chromophoric resin ingredient. U.S. Pat. No. 3,699,135 describes a polymer dye prepared by the copolymerization of a silane with an anthraquinone containing two aliphatic hydroxyl groups. U.S. Pat. No. 4,375,357 describes water-soluble noncrystalline polymer block colorants composed of an organic polymer backbone with pendant azo chromophoric units.
Other prior art publications which describe polymeric dyes for toner compositions include U.S. Pat. Nos. 3,553,133; 4,645,727; 4,778,742; 5,200,290; 5,212,033; 5,296,325; and 5,437,953; incorporated by reference.
There is continuing interest in the development of new and improved toner compositions for application in electrophotography.
Accordingly, it is an object of this invention to provide a polymeric dye toner composition which has a superior combination of properties for electrophotographic imaging systems.
It is another object of this invention to provide chromophoric monomers which are adapted for preparation of polyester dyes by a copolymerization reaction.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.